Monochlorosilane (formula ClSiH3, henceforth MCS) has been identified as a promising precursor to low temperature silicon nitride film deposition in microchip fabrication.
MCS is stored in sealed containers as a liquid under its own vapor pressure (74 psig at 68° F., 612 kPa at 20° C.). Steel containers are used to contain the vapor pressure of the MCS and are required by code for its transportation.
High quality silicon nitride film deposition processes require precursors having consistently high purity. However, MCS has been found to decompose rapidly to dichlorosilane (formula H2SiCl2, henceforth DCS) and monosilane (henceforth SiH4) in the metal containers at ambient temperature (20° C.). Decomposition products represent “impurities” in the MCS. DCS present in trace amounts is particularly deleterious in the nitride film deposition process. Furthermore, variation in the DCS content of MCS delivered from storage containers adversely affects the deposition process stability. The amount of impurities in MCS extracted from the container can vary significantly over time. This variation results from a combination of MCS decomposition and vapor/liquid phase partitioning of the impurities. The amount of impurities in the container at a given time is determined by the decomposition rate and the storage time.
Extraction of MCS from the container typically occurs from the vapor phase at the top of the container. However, due to the disparate boiling points of MCS and impurities in the mixture, lower boiling point compounds, such as MCS and SiH4 impurity, tend to predominate in the extracted vapor, while higher boiling point compounds, such as DCS, are preferentially partitioned to the liquid phase.
As a result, DCS becomes concentrated in the container's “liquid heel” over time. DCS levels in the extracted vapor therefore rise as MCS is removed from the container causing a variation in MCS purity. Since high consistency in MCS purity is required for deposition of quality nitride thin films, it is important to minimize the rate of MCS decomposition during storage. This in turn minimizes the increase in DCS levels during MCS extraction from the container.
Prior art in the general field of the present invention includes:    US 2003/0068434;    U.S. Pat. No. 5,009,963;    U.S. Pat. No. 5,480,677;    U.S. Pat. No. 5,259,935;    U.S. Pat. No. 5,479,727;    U.S. Pat. No. 2,900,225;    U.S. Pat. No. 3,968,199;    Su, Ming-Der and Schlegel, Bernhard “An ab Initio MO Study of the Thermal Decomposition of Chlorinated Monosilanes, SiH4-nCln (n=0-4)”, J. Phys. Chem. 1993, 97, 9981-9985;    Walker, K. L., Jardine, R. E., Ring, M. A. and O'Neal, H. E., “Mechanisms and Kinetics of the Thermal Decompositions of Trichlorosilane, Dichlorosilane, and Monochlorosilane”, Int. J. Chem. Kinet 1998, 30, 69;    Swihart, Mark T. and Carr, Robert W., “On the Mechanism of Homogeneous Decomposition of the Chlorinated Silanes. Chain Reactions Propagated by Divalent Silicon Species”, J. Phys. Chem. A 1998, 102, 1542-1549;    Walch, Stephen and Datco, Christopher, “Thermal Decomposition Pathways and Rates for Silane, Chlorosilane, Dichlorosilane, and Trichlorosilane”, J. Phys. Chem. A 2001, 105, 2015-2022;    Nitodas, Stephanos F. and Scotirchos, Stratis V., “Methematical Modeling of the Gas-Phase Chemistry in the Decomposition of Chlorosilanes in Mixtures of Carbon Dioxide and Hydrogen at High Temperatures”, J. Electrochem. Soc., 149 (2) C112-C119 (2002);    Vaughan, Stephen, “Nitric Oxide and Nitrogen Dioxide Gas Standards”, Gases and Instrumentation, November/December, 2007;    Guangquan Lu, Rubloff, G. W. and Durham, J. “Contamination Control for Gas Delivery from a Liquid Source in Semiconductor Manufacturing”, IEEE Transactions on Semiconductor Manufacturing, 10(4), 425-432, (1997);